A display device with photosensors that can detect the brightness of ambient light or scan an image of an object placed near the display has been disclosed. Such a display device achieves these functions by having photosensors such as photodiodes, for example, incorporated in a pixel region thereof. In recent years, in particular, there is an increasing demand for a so-called scanner function that makes it possible to read an image from a document and the like placed on the front surface of the display of the display device with photosensors.
A conventional display device with photosensors that can read an image is disclosed in Japanese Patent Application Laid-Open Publication No. 2004-153329, for example.
In the display device with photosensors having a scanner function, an image for one frame is composed based on outputs from a plurality of photosensors disposed in the pixel region. Therefore, it is necessary to have an image memory that can store data for one frame.